An important problem in Quantum Information is the transfer of states with high fidelity between locations. The devices performing this function are referred to as quantum wires. Spin chains can in principle be used to construct such wires. I shall discuss the design of spin chains that realize perfect and almost perfect transfer, that is that transport a state from one end of the chain to the other with probability one or almost one over some time.

Orthogonal Polynomial Theory and elements of Diophantine approximation will be called upon.